Re: Strange scans - inquisitive question

[paul.rogers () MIS-CDS COM (Paul Rogers)]

I thought that would be the answer - thanks. But surely if they were
"scanning", we wouldn't get 10,000 connections from a host in one "session".
When the source is allegedly a dialup host, this sort of "scanning" would
surely flood their connection?

It's just annoying because the log files start getting large and are a pain
to sort through.

Cheers,

Paul Rogers,
Network Security Analyst.

MIS Corporate Defence Solutions Limited

Tel:            +44 (0)1622 723422 (Direct Line)
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> -----Original Message-----
> From: Valdis.Kletnieks () vt edu [mailto:Valdis.Kletnieks () vt edu]
> Sent: 12 June 2000 05:31
> To: Paul Rogers
> Cc: INCIDENTS () SECURITYFOCUS COM
> Subject: Re: Strange scans - inquisitive question
>
>
> On Fri, 09 Jun 2000 10:46:21 BST, Paul Rogers
> <paul.rogers () MIS-CDS COM>  said:
> > Last night we received some strange scans with a source
> port of 21 (ftp) and
> > a destination port of 7 (echo). The destination address was
> always the
> > network address. I was just wondering if anyone else had
> seen these scans or
> > whether anyone knew what they were looking for. The scans
> were performed
> > over TCP (protocol 6) and UDP (protocol 17).
>
> Well.. the destination port 7 (echo) over TCP and UDP is pretty
> obviously just scanning your net looking to see what machines answer.
>
> Why source of 21?  To fool firewalls into thinking that it's an
> FTP connection, and that the packet in question is a return packet
> for something you sent to their well-known-port.
>
> Yes, that only works for TCP, since FTP doesn't run over UDP,
> but there's probably enough firewalls out there that blindly
> allow port 21 traffic without further sanity checking that using 21
> as the source port is A Big Win for the scanner...
>
>                               Valdis Kletnieks
>                               Operating Systems Analyst
>                               Virginia Tech

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